Gerry Adams, the Sinn Féin leader and chief architect of the Irish republican movement's peace strategy, has been arrested by police over a notorious Troubles murder that has haunted his political career for decades.

The veteran Sinn Féin president put himself forward for questioning by the Police Service of Northern Ireland (PSNI) in connection with the kidnapping, killing and secret burial of Jean McConville.

The family of the widowed mother of 10, whom the IRA "disappeared" just before Christmas 1972, welcomed the arrest and said they hoped it would lead to the whole truth ultimately being exposed about their mother's murder.

But Sinn Féin's deputy leader, Mary Lou McDonald, who sits alongside Adams in the Irish parliament, described the arrest of her fellow TD (MP) as politically motivated after a "concerted and malicious effort to link Gerry Adams to this case for considerable time".

A spokesman for the Northern Ireland Office rejected the suggestion that the arrest was politically motivated. The spokesman said: "This is entirely an operational matter for the PSNI."

A PSNI spokesman said: "Detectives from the serious crime branch investigating the abduction and murder of Jean McConville in 1972 have arrested a 65-year-old man in Antrim. The suspect is currently being interviewed by detectives at the serious crime suite in Antrim police station."

Just before Adams walked into the police station on Wednesday evening, he denied to RTÉ television that he had anything to with the McConville murder. Adams also rejected recent claims by former IRA bomber and convicted killer Peter Rogers that he and the Sinn Féin deputy first minister Martin McGuinness had ordered him to transport explosives to bomb Britain in 1980.

In a statement issued shortly after it was announced that he had been arrested, Adams said: "I believe that the killing of Jean McConville and the secret burial of her body was wrong and a grievous injustice to her and her family.

"Well-publicised, malicious allegations have been made against me. I reject these. While I have never disassociated myself from the IRA and I never will, I am innocent of any part in the abduction, killing or burial of Mrs McConville."

The arrest of Adams follows the decision of a US court to compel a US university to hand over a series of tape recorded interviews with former republican paramilitaries. The Boston College Belfast Project tapes, which also include frank testimonies from former loyalist paramilitaries, were only meant to have been made public once an individual who gave candid interviews about their role in political violence had died.

In an interview published posthumously, Adams's former comrade and close friend, the late Belfast IRA commander Brendan Hughes, alleged that the future Sinn Féin president gave the order for Jean McConville to be "disappeared" by a specialist IRA unit that the future Sinn Féin chief set up to weed out informers within the nationalist community in the city. Adams has denied not only being involved in the McConville murder but that he was ever a member of the IRA.

The arrest of Adams is an acutely sensitive matter – a point highlighted by Sinn Féin, which suggested that the move was designed to damage the party on the eve of the European parliamentary elections. Alex Maskey, a veteran Adams ally who sits in the Northern Ireland assembly, told Newsnight on BBC2: "Let's remember that Gerry Adams voluntarily made arrangements to speak to the PSNI and then he has been arrested in such a public fashion. We believe there is a political agenda here … We are now three weeks into an election and we believe there is a very negative agenda."

Jean McConville was 'disappeared' by the IRA in 1972 on suspicion of being an informant. Photograph: PA Pa/PA

The government will say that all decisions on the Adams case are taken independently of ministers. Any decision to charge Adams would be taken by Barra McGrory QC, the director of public prosecutions in Northern Ireland, who has acted on behalf of Sinn Féin in the past and who has a reputation for being scrupulously fair.

McConville was torn away from her 10 children at their home in the Divis flats complex in west Belfast in December 1972. The IRA put out a bogus story that she had later run away to England and had abandoned her children. They also alleged that the 37-year-old Protestant-born widow was an informer, which the then Northern Ireland police ombudsman Nuala O'Loan later concluded was untrue.

It was not until 1999 that the IRA finally admitted they had abducted, killed and buried her on a beach in Co Louth, across the border in the Irish Republic.

Ivor Bell, another of Adams's one-time republican comrades who, like Hughes became a bitter critic of the Sinn Féin's president, is currently on bail facing charges in connection to the McConville murder. Bell faces charges of aiding and abetting the killing. Bell, who was expelled from the IRA in the early 1980s after being accused of attempting to stage an internal coup against its leadership, denies all the charges.

One of McConville's children who witnessed her abduction in front of several male and female IRA members, Helen McKendry, told the Guardian she and her husband Seamus were "pleasantly optimistic" that justice would finally be done for her mother.

Seamus McKendry, who along with his wife started the campaign in 1994 to highlight the plight of the Disappeared – the 16 IRA victims shot and buried in secret during the 1970s and 80s – said: "The family are quite happy that Adams is being questioned about Jean's murder. But even if this inquiry fails we have always made clear that we will pursue a civil legal action against Adams."He said: "It should be noted that the IRA and people in Sinn Fein like Mr Adams always insisted that this was a war. Under the Geneva convention to 'disappear' someone in a war is a war crime. He should keep that in mind in these days ahead because it has long been our view that what happened to Jean was a war crime."

McKendry and his wife said Adams facing questions over the murder vindicated the PSNI's pursuit of the Belfast Project Tapes. A number of people have already been arrested and questioned in relation to the McConville killing after the PSNI was able to seize taped testimony from IRA veterans who talked openly to the project about their role in the armed campaign, including the murders of the Disappeared. The tapes were only meant to have been made public once the person who had given candid testimony about their role in the violence had died.

McKendry said the PSNI's decision to go after the material in the US courts had been justified.

"We had insisted that the police go after every small piece of the jigsaw in relation to Jean's disappearance and murder. That is why it was right to pursue those tapes. What the family now hope and pray for is that Jean's grandchildren do not have to pass on this fight for justice onto the next generation."

Why now?

It was a court decision in the US that led to the Sinn Féin president being interviewed by police. In 2001, Boston College commenced a five-year oral history project aimed at documenting perspectives on the Troubles from those involved in the conflict.

Academics, historians and journalists interviewed former paramilitaries, both republican and loyalist, about their roles in the 40 years of violence that blighted Northern Ireland. The participants took part on the undertaking that their accounts would only be made public upon their death.

When one such interviewee, former IRA commander in Belfast Brendan Hughes died in 2008, his tapes contained an allegation that Adams was a senior IRA leader during the Troubles and that he had ordered McConville's killing – claims that the Sinn Féin leader vehemently contested.

Prior to her death last year, Old Bailey bomber Dolours Price made further allegations separate to the Boston College project. Again the Louth TD rejected the claims.

The revelations prompted lawyers representing the PSNI to launch a legal bid in the US to obtain the relevant Boston College tapes. A court battle ensued, but last year the PSNI won and the college was ordered to pass over the tapes.

Having taken time to examine their contents, detectives have ramped up their investigation in the last two months, making a series of arrests. In March veteran republican Ivor Bell, 77, from Ramoan Gardens in the Andersonstown district of west Belfast, was charged with aiding and abetting in the murder – a count he denies. Five others have been detained and questioned by detectives, culminating in the arrest of Adams.